WO 01/95471 A1, which is incorporated herein by reference, describes a method for determining the rotary position of the drive shaft of a DC motor, in which method the current ripple (actual current ripple) is evaluated. To this end, a suitable reference current ripple is compared with the actual current ripple which is measured during operation of the motor.
DE 42 32 130 A1, which is incorporated herein by reference, discloses a circuit arrangement with which, in an ABS brake control device, the generator voltage of a DC pump motor may be determined during a pulse-width-modulated (PWM) drive operation. The delivery rate of the hydraulic pump is controlled with the aid of the generator voltage. However, the current ripple is not evaluated in this case. Evaluation of the generator voltage for determining the pump rotation speed in an ABS control device is also described in DE 103 55 239 A1, which is incorporated herein by reference. In this document, the rotation speed is controlled with the aim of allowing the valves to be driven in a noise-optimized manner. Finally, the hydraulic pressure generated by the pump is also indirectly determined here.